DØ Event 417 The Gold Plated Top Event* Finding a “Golden” Event D0 Side View 3-AUG-1993 23:34 Run 58796 Event 417 10-JAN-1993 02:41 MUON ELEC TAUS VEES OTHER + ++ ++ + ++ ++ + + ++ + + + + ++ + + + + ++ + ++ ++ + + + ++ ++ + + + + + ++ + + + ++ ++ + ++ ++ + + ++ + + + + ++ + + + + ++ + ++ ++ + + + ++ ++ + + + + + ++ + + 0.3 <E< 1.4 1.4 <E< 2.3 2.3 <E< 3.3 3.3 <E< 4.3 4.3 <E Event has Spurious A Layer Hits Muon Track Hits Dave Hedin blew up the view of the muon hits to about 10 feet. He measured the track with meter sticks on his basement floor at home. He also redid the alignment. He calculated the momentum with and without the A layer hits. The fit with the A layer needed large multiple scatters in the calorimeter and magnet iron and had low probability. Muon Daria Zieminska and Dave Hedin exchanged ~30 e-mail messages on the fits for this track to determine the muon momentum more precisely. Using fits by hand and prototype computer code they determined the muon momentum to be greater than 100 GeV/c . Background Probabilities Top Quark Mass from Event 417 ---------------------------------------------------- Sample Logbook Pages Sample Logbook Pages: * In 1993, while scanning the express stream, Boaz Klima found event 417, which had an very high E T electron, a high p T muon, 3 jets and large missing E T, making it an outstanding candidate for a top event, since expected are small. Event 417 failed the original top selection because spurious muon A-layer hits gave the muon track very low momentum. This can be seen in the end view (below). Other aspects of this event were checked by many experts to see that all other systems worked properly. Kinematic Parameters of Event 417 DST LEGO 3-AUG-1993 23:39 Run 58796 Event 417 10-JAN-1993 02:41 MUON MUON ELEC Miss ET PHYDIS ETMIN= 1.00 2 MUON 1 MISS ET 1 ELEC 3 JET (HAD) (EM) 2 MU TK E e T = 98.8 ± 1.6 GeV p µ T = 195 GeV/c E j1 T = 24.9 ± 4.3 GeV E j2 T = 22.3 ± 5.6 GeV E j3 T = 6.7 ± 3.6 GeV Missing E T = 102 GeV This event survived the final Run 1 cuts, since it has such high momentum and missing E T . Note: This is a personal view of finding and interpreting aspects of the most spectacular top candidate event in DØ. The full task of assembling and analyzing the complete top quark sample required the dedicated talents of a much broader group of people. Sharon Hagopian muon electron backgrounds (>40 GeV/c at 95% CL) Suman Beri, Puspha Bhat, Jim Cochran, and Harrison Prosper were among those who worked on calculating the probabilities for this event to be produced by various background processes. The probability was 10 to 1 that this event was top. Event 417, which was the world’s first observed top event, was presented at conferences in 1993. Ulrich Heintz, Raja, and Mark Strovink worked on a likelihood calculation, based on a method inspired by Dalitz, Goldstein, and Kondo, which determined that the event was consistent with top masses of 100-200 GeV/c 2 . The likelihood was maximized at mass(top) =145 GeV/c 2 . Later, Harrison Prosper calculated the top mass for event 417 using a new kinematic method. He estimated that the mass(top) =163 ± 36 GeV/c 2 . Publication The parameters of Event 417 and likelihood mass determination was submitted for publication at the end of 1993 and appeared in a PRL article entitled “Search for the Top Quark” in April, 1994. This event also survived later, tighter cuts, and was included in the final DØ Run I dilepton results, published in 1998. (First two pages from the logbook of Dave Hedin and last three pages are from the logbook of Harrison Prosper.)